Presence of vasoactive intestinal peptide receptors coupled to adenylate cyclase in rat lung membranes

Abstract

(1) The binding of 125I-labelled vasoactive intestinal peptide (VIP)_ to a particulate fraction from rat lung was rapid, temperature dependent, saturable and specific. This process was also reversible and 125I-labelled VIP dissociation was accelerated by guanine triphosphate nucleotides. The curves describing the inhibition of tracer binding by peptides of the VIP-secretin family suggested the presence of at least two classes of VIP receptor: a ‘high- affinity’ type with decreasing affinity for VIP in the order: VIP = [Val 5]secretin > [Ala 4, Val 5]secretin; and a ‘low-affinity type’ with decreasing affinity for VIP in the order: VIP > [Val 5]secretin > [Ala 4, Val 5]secretin = secretin > [Ala 4]secretin. (2) VIP and related peptides stimulated the adenylate cyclase activity of the same lung membrane preparation more efficiently than β-adrenergic agonists and prostaglandins E 1 and E 2. The dose-effect curves of stimulation of adenylate cyclase by VIP and parent peptides were also compatible with the existence of two classes of VIP receptor, the relative peptide potencies being identical with their relative ability to compete with 125I-labelled VIP for binding.